The present invention relates to a molded cap for insulating series loop connections on bar wound armatures of electrical systems, for example, generators, and particularly relates to a pair of homomorphic sections for assembly to form a cap enclosure of selected width to accommodate variations in series loop dimensions which would otherwise require caps of different sizes.
Molded caps for insulating series loop connections in electrical systems, for example, turbo-generators, have recently, in many applications, replaced resin-filled mica tapes previously wrapped about the series loop connections. Notwithstanding the use of new molded caps for this purpose, electrical systems, including generators, are currently being designed with series loops on their armatures having shapes which are very difficult to tape or accommodate in a particular molded cap. While the caps have afforded large cost savings in time and materials and higher quality series loops, the molded caps heretofore have the disadvantage that different size caps are required for different size series loop connections. This has led to high tooling costs to make caps of different sizes and, as a consequence, the molded caps, while an improvement over the resin-filled mica tapes, have been applied only to high-production electrical systems. Stated differently, because of the lack of dimensional commonality in electrical systems design, the application of a particular sized cap to series loops is limited. At the same time, it has become increasingly desirable to apply molded caps to conventional electrical systems such as generators, including older generators when they are rewound.
Conventional molded caps are essentially five-sided boxes each having a pair of opposed side walls, an end wall, and covers spaced one from the other along opposite sides of the cap, leaving an open end through which the loop may be received. The caps are conventionally molded from glass-reinforced thermoset materials. To install these conventional caps, they are generally filled with a thermoset potting compound and pushed over the series loop. In certain instances, the potting compound is injected into the cap after it has been placed on the series loop.
A clamshell-type cap has also recently been designed and has the advantage of requiring less filler material and a less massive series loop. However, the clamshell design is less versatile than the conventional molded cap and is generally contoured around the series loop such that relatively little variation in loop size may be accommodated. Because it cannot be pushed axially over the series loop as a conventional cap, additional clearance between adjacent series loops is necessary. Significantly, tooling costs are much higher for the clamshell-type cap because the two halves require two different molds.
According to the present invention, there is provided a molded cap formed of two identical or homomorphic cap sections which, during assembly to form a series loop cap enclosure, are adjustable in width to form a cap enclosure for receiving a number of different sized series loops. For example, while the length and height of the series loops are very closely related, the width of the loops vary greatly between otherwise similar designs and particularly vary according to the type of the series loop connection. For example, a series loop with a strand-to-strand braze is much narrower than a series loop with a single-shot braze connection, the latter being about twice as wide as the strand-to-strand braze, although their length and height dimensions are similar. Thus, the present invention provides a molded cap formed of two identical cap sections which, during assembly, are adjustable in width to accommodate different designs of series loops.
To accomplish those ends, two identical cap sections, formed of dielectric material, are assembled together to form a five-sided enclosure with an open end for receiving the series loop. Each cap section includes a pair of spaced side walls, an end wall interconnecting the side walls at one of the section and a cover extending between the side walls and from the end wall along one side of the cap section, leaving free the margins of the side and end walls along the opposite side of the cap section. To permit assembly of the two cap sections to form the cap, each end wall has first and second generally parallel segments offset longitudinally one from the other. These segments have edges inset from the free margin of the end wall at a location substantially medially of the length of the end wall to define an inset portion or opening extending at least equal to one half the depth of the end wall. Additionally, a longitudinally extending tab is disposed adjacent to one of the side walls in generally parallel relation therewith and adjacent the end wall to define a slot with the one side wall for receiving an opposite side wall portion of the other cap section when the cap sections are assembled. A rib also projects inwardly from the opposite side wall at a location from the end wall a distance in excess of the length of the tab. The tab has an opening and the opposite side wall has an opening for facilitating securement of the sections one to the other as set forth hereinafter.
To assemble the cap sections to form the cap, the side walls and end wall segments are respectively intermeshed or nested whereby the cap sections in final assembly are transversely offset a distance corresponding substantially to the width of a side wall while simultaneously aligned in the longitudinal direction. Thus, the side walls of a first cap section lie in generally parallel juxtaposition with the respective side walls of the second cap section. More particularly, the first side wall of the first cap section lies outwardly of the corresponding second side wall of the second cap section while the second opposite side wall of the first section lies inwardly of the first opposite side wall of the second section. Additionally, the second side wall of the first cap section has a portion which lies between the first side wall and tab of the second cap section while the second side wall of the second section has a portion which lies between the first side wall and tab of the first cap section. The first and second end wall segments of the first section lie in side-by-side generally parallel relation with the respective second and first end wall segments of the second section. The inset edges of the first and second segments of each end wall defining the inset portion medially of the length of the end wall enable an intermeshing of the first and second segments of the end walls of the respective cap sections and the respective side walls. The covers of the first and second sections lie in spaced opposition one to the other. Thus, the covers, side walls and end walls define a generally five-sided enclosure open at an end thereof opposite the end walls for receiving the series loop of the armature.
It will thus be appreciated that, when assembling the cap sections, the covers may be selectively spaced one from the other, depending upon the extent to which the side walls and end walls intermesh. Thus, the cap sections can be disposed in close-fitting intermeshed and/or interdigitated relation one to the other for receiving a relatively narrow series loop with strand-to-strand braze or can be formed to a wider configuration for receiving the wider series loop with single-shot braze. Of course, different configurations of loops, as well as different thicknesses of loops can likewise be accommodated.
To mechanically lock the two cap sections one to the other, potting resin is disposed within the cap sections and fills the openings in the tabs and opposite side walls. The potting resin in those openings forms locking pins which hold the cap sections captive to one another in the event of a bond failure.
Additionally, the cap sections may be assembled prior to assembly over the loop or they may be assembled as a clamshell-type cap. Thus, the potting resin may be disposed in the two cap sections and the sections assembled together and subsequently pushed over the series loop. Alternatively, the cap sections may be closed about the loop, as in a clamshell configuration. The cap sections may be temporarily held together with spring clamps or large rubber bands while the potting resin cures. Alternatively, the cap may be tied in a closed condition with permanent banding tape serving to lock the cap on the loop.
In a preferred embodiment according to the present invention, there is provided a cap for disposition on the series loop of a bar wound armature of an electrical system, comprising first and second substantially identical cap sections, each section having (i) first and second opposed generally parallel longitudinally extending side walls, (ii) an end wall extending generally transversely between the side walls adjacent one end of the section and (iii) a cover extending between the side walls and from the end wall along one side of the cap section leaving free the margins of the side and end walls along the opposite side of the cap section. Each end wall has first and second generally parallel segments offset one from the other in the longitudinal direction with the second segment being inset longitudinally from the first segment, each first end wall segment extending from the first side wall generally transversely toward the second side wall, each the second end wall segment extending from the second side wall generally transversely toward the first side wall, the first and second segments having edges inset from the free margin of the end wall at a location therealong intermediate the side walls. The first and second sections are assembled to form the cap with (i) the first and second side walls of the first section lying generally parallel and side-by-side with the respective second and first side walls of the second section, (ii) the first and second end wall segments of the first section lying in side-by-side generally parallel relation with the respective second and first segments of the second section, and (iii) the covers of the first and second sections spaced one from the other on opposite sides of the cap whereby the covers, the side walls and the end walls define an enclosure open at the end thereof opposite the end walls for receiving the series loop of a bar wound armature. The inset edges of the first and second segments of the first section and the inset edges of the first and second segments of the second section enable the respective side walls of the first and second cap sections and the respective end wall segments thereof to intermesh and thereby form the cap.
In a further preferred embodiment according to the present invention, there is provided a cap enclosure portion for disposition on the loop of a bar wound armature of an electrical system, comprising a cap section having (i) a pair of opposed generally parallel longitudinally extending side walls, (ii) an end wall extending generally transversely between the side walls adjacent one end of the section and (iii) a cover extending between the side walls and from the end wall along one side of the cap section leaving free the margins of the side and end walls along the opposite side of the cap section. The end wall has first and second generally parallel segments offset one from the other in the longitudinal direction with the second segment being inset longitudinally from the first segment, the first and second end wall segments each extending transversely from a respective side wall generally toward the opposite side wall. The first and second segments have edges inset from the free margin of the end wall and define an opening in the end wall and which opening opens through the margin of the end wall, the section further including a longitudinally extending tab spaced closely adjacent and substantially parallel to one of the side walls to define a slot therewith having a width at least equal to the width of the opposite side wall section.
In a further preferred embodiment according to the present invention, there is provided a cap for disposition on the loop of a bar wound armature of an electrical system, comprising first and second substantially identical cap sections, each section having (i) a pair of opposed generally parallel longitudinally extending side walls, (ii) an end wall extending generally transversely between the side walls adjacent one end of the section and (iii) a cover extending between the side walls and from the end wall along one side of the cap section leaving free the margins of the side and end walls along the opposite side of the cap section. Each end wall has first and second generally parallel segments offset one from the other in the longitudinal direction with the second segment being inset longitudinally from the first segment, the first and second segments having edges defining a portion inset from the free margin of the end wall and disposed substantially medially of the end wall, the first and second sections being assembled to form the cap with (i) the side walls of the first section lying in generally parallel juxtaposition with the respective side walls of the second section, (ii) the first and second end wall segments of the first section lying in side-by-side generally parallel relation with the respective second and first segments of the second section, and (iii) the covers of the first and second sections lying in spaced opposition one to the other whereby the covers, the side walls and the end walls define an enclosure open at the end thereof opposite the end walls for receiving the loop of the bar wound armature, the inset portions of the first and second cap sections enabling offset intermeshing of the sections in a transverse direction when assembled to form a cap.
Accordingly, it is a primary object of the present invention to provide a novel and improved cap for enclosing series loops of an armature in an electrical system wherein the cap is formed of two identical sections from a single mold and which cap sections can be readily and easily assembled in intermeshed transversely offset and longitudinally aligned relation to one another to define a cap having a selected width whereby series loops of different sizes, particularly widths may be accommodated.
These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings.